CORE B ABSTRACT The Program Project (P01) entitled ?Delirium, Dementia and the Vulnerable Brain: An Integrative Approach? seeks to define the complex relationship of delirium, dementia, and brain vulnerability through a series of five, interrelated projects, each of which examines a unique aspect of vulnerability. The Field Core will support all of the projects and has the following Specific Aims: Aim 1: To perform assessments on the original Successful Aging after Elective Surgery (SAGES I) cohort free of dementia at baseline (N=560), ensuring the highest possible participant retention and completeness of study variables. Activities include: 1) For the entire SAGES I cohort, completing two waves of long-term follow-up interviews: the first wave (years 1-3) will ensure a minimum of 5 years of follow-up, and the second wave (years 3-5) will ensure a minimum of 8 years of follow-up; 2) Inviting 128 SAGES I participants, probability sampled based on their index admission delirium status and frequency matched by age and baseline cognitive status, to return to the hospital for a detailed evaluation, including cerebrospinal fluid (CSF) collection via lumbar puncture (LP) for Alzheimer's Disease (AD) and inflammatory biomarker measurement, phlebotomy for plasma AD and inflammatory marker measurement, magnetic resonance imaging (MRI) studies, and transcranial magnetic stimulation (TMS)-electroencephalography (EEG) studies. Aim 2: To accrue a new cohort, called SAGES II, of 400 patients undergoing total hip or knee replacements under spinal anesthesia at two academic medical centers, Beth Israel Deaconess Medical Center (BIDMC) and Brigham and Women's Hospital (BWH), and to follow this cohort for 18 months with extended follow-up to 36 months. Activities related to the SAGES II cohort include: 1) identifying, approaching, and enrolling eligible patients with a goal of achieving the highest possible participation; 2) performing baseline assessments prior to surgery, in-hospital assessments for delirium daily throughout the index hospitalization, and follow-up assessments at 1, 2, 6, 12, 18, months after surgery, with extended follow-up at 24 and 36 months; 3) providing specialized support for each of the component projects by collecting CSF and blood samples for AD and inflammatory biomarker measurement, and referring patients for MRI, TMS, and EEG studies. Aim 3: To hire, train, and monitor the activities of all field staff, ensuring coordination of all aspects of the SAGES I and II cohort studies including study participant safety, and high quality data collection. Through execution of these Aims, the Field Core will play an essential role in all aspects of the Program Project, which will define the complex relationship of delirium, dementia, and brain vulnerability. The Field Core has been highly successful in achieving all of its Aims in the first funding cycle. In the renewal, we will implement the same principles and procedures, employ many of the same leaders and field team staff members. This continuity ensures a very high likelihood of continued success.